Optically readable tags are markers containing specific patterns or geometric primitives that can be detected and read by an optical sensor such as a camera. One application of optically readable tags is to allow the identification of items in scenarios such as warehouses, for example, in an electronic commerce fulfillment center, or in archives such as a library. Optically readable tags allow items such as boxes, packages, books or shelves to be quickly identified in an automated manner.
In recent years, the above scenarios are increasing becoming automated, with robotic pickers automatically fulfilling electronic commerce orders. Therefore, there is increasing demand for optically readable tag systems.
Examples of existing two-dimensional visual marker systems include Barcodes, which are described in U.S. Pat. No. 2,612,994, PDF417 type, stacked linear barcodes which are described in U.S. Pat. No. 5,243,655, Quick Response Codes (QR Codes) by Denso Wave which are described in U.S. Pat. No. 5,726,435, High Capacity Color Barcode (HCCB) by Microsoft, DataMatrix, Aztec Code, and MaxiCode. These markers are mainly intended to carry as much information as possible. However, they can be decoded only at a close distance and are ill-suited for long distance decoding. Here, close distance means a distance of <20 cm. To scan through each and every item utilising such codes is a tedious and time-consuming process.
In scenarios such as electronic commerce fulfillment and inventory management, for example in a library, there is a demand for markers that can be read at variable distances, for example from 20 cm to 150 cm. There is also a requirement for a marker system that can be read from a range of distances and camera orientations. Many of the marker systems discussed above are only readable within a short distance and with specific camera orientations relative to the marker.